Because it affects almost every aspect of our understanding of active galactic nuclei (AGNs), knowing the total reddening of an AGN is crucial. The majority of studies of the spectral energy distributions (SEDs) and broad-line intensities of type-1 thermal AGNs assume that reddening other than by dust in our solar neighbourhood (typically \(E(B-V) < 0.05\)  for high Galactic latitude directions) is negligible. On the other hand, other studies have pointed to substantial reddenings in some AGNs (\(E(B-V) \sim 0.2\)  and higher – see [1]} for a review). There are two main reasons why many researchers have assumed that internal reddening is low. The first is that there is only a small amount of additional reddening (\(E(B-V) \sim 0.03 - 0.05\) ) associated with the high-velocity outflows seen in broad absorption line quasars (BALQSOs), and the dust associated with the outflows has a reddening curve that rises strongly going into the UV like the reddening curve of the Small Magellanic Cloud (SMC) bar (see Figure 5 of [2]}). If \(E(B-V) > 0.1\) , and if the SMC-like reddening curve of BALQSOs is applicable to AGNs in general, the SED of AGNs should fall rapidly going into the far UV. This is seen only rarely. The second reason for thinking that the reddening of AGNs is low is that it has long been thought that in the broad-line region (BLR) of AGNs, Lyman \(\)  is suppressed and the H\(\) /H\(\)  ratio increased by collisional and radiative transfer effects (e.g., [3]}; for a review see [1]}). If this is the case, observed Ly\(\) /H\(\)  and H\(\) /H\(\)  ratios imply little or no reddening.
